Conventionally, a fuel supplying device includes a fuel tank accommodating fuel, a supply pump drawing the fuel from the fuel tank and supplying the fuel to an internal combustion engine, and a fuel filter provided in a passage between the fuel tank and the supply pump to filter the fuel. The fuel filter prevents foreign matters from flowing to the supply pump and parts of the internal combustion, by removing the foreign matters in the fuel.
Since the fuel filter continuously removes the foreign matters in the fuel, the fuel filter may be clogged. When the fuel is supplied in a case where the fuel filter is clogged by the foreign matters, the foreign matters block a flow of the fuel. Therefore, it is necessary to detect a clogging of the fuel filter at an early stage and exchange the fuel filter, so as to ensure a reliability of the fuel supplying device.
Generally, a viscosity of the fuel varies in accordance with a fuel temperature. For example, when the fuel temperature is low, a high-viscosity change of the fuel is generated. The high-viscosity change of the fuel is a change of the viscosity of the fuel from a low viscosity to a high viscosity. When the fuel of the high viscosity is filtered by the fuel filter, the fuel is remarkably affected by a flow resistance of the fuel filter according to the high viscosity. Therefore, even when the clogging of the fuel filter is not generated by the foreign matters, the flow resistance may be detected as the clogging of the fuel filter. To avoid detecting the clogging according to the high-viscosity change of the fuel, it is known that a non-detection period where a clogging detection is prohibited is set until the high-viscosity change of the fuel is canceled by increasing the fuel temperature.
A method for determining that the high-viscosity change of the fuel is canceled by increasing the fuel temperature is necessary to set the non-detection period. To monitor an increase in fuel temperature, a temperature sensor provided in an inlet portion of the fuel filter and detecting the fuel temperature is known. When a detected temperature reaches a temperature where the high-viscosity change is canceled, it is determined that the high-viscosity change is canceled. However, since it is necessary to mount the temperature to the inlet portion of the fuel filter, a number of parts increases, and a cost increases. To monitor the increase in fuel temperature without the temperature sensor, JP-2005-273535A discloses a fuel supplying controller to set the non-detection period. Further, a count is started since a start of the internal combustion engine, and a count value is added to a timer counter in case where a vehicle speed exceeds a threshold. When the timer counter exceeds the non-detection period, it is determined that the high-viscosity change of the fuel is canceled, and then the clogging detection of the fuel filter is executed.
Generally, a temperature of the internal combustion engine is increased by a combustion of the fuel, even though the internal combustion engine operates in a steady state such as idling operation. A return fuel returned from the internal combustion engine to the fuel tank receives heat generated by combusting other fuel in the internal combustion engine, and the fuel temperature of the return fuel increases. The fuel temperature in the fuel tank is increased by the return fuel. Thus, the fuel temperature of the fuel flowing through the fuel filter may increase even in the steady state. In the fuel supplying controller, the count is executed in a case where the vehicle speed exceeds the threshold (e.g., zero) that is predetermined. In the steady state where the vehicle is not travelling, such as a case where the internal combustion engine operates in the idling operation, the vehicle speed does not exceed the threshold. In this case, the count is not executed in the steady state, and the timer counter does not exceed the non-detection period. Even when the fuel temperature increases to cancel the high-viscosity change of the fuel in the steady state, the clogging detection of the fuel filter is not started.
Further, in a case where the steady state and an unsteady state such as a travelling of the vehicle are repeated, an exceeding period for the timer counter to exceed the non-detection period since the start of the internal combustion engine may become longer because a count of the timer counter is not executed in the steady state. Therefore, when the vehicle operates in a short term, it is possible that the timer counter does not exceed the non-detection period and the clogging detection is not started.
When the clogging detection is not started, the clogging of the fuel filter generated by the foreign matters cannot be detected, the fuel is not properly supplied, and a reliability of the fuel supplying device is deteriorated.